Most earth moving equipment vehicles such as bulldozers generally includes a chassis, a variety of front-mounted blades, protective driver cabin, a hatch and a form of access or access system. The chassis includes all the mechanical parts that form the structural frame of the earth moving equipment vehicle. The driver operates the earth moving equipment vehicle from the protective driver cabin. A hatch is located behind the driver cabin and typically houses many of the important control units of the earth moving equipment vehicle such as hydraulic controls, hydraulic pump, fuse box, electrical circuit breakers etc. The form of access or access devices provides access between the ground level and the cabin. Walkways are provided around the cabin area for an operator to access the hatch located behind the driver cabin of the earth moving equipment vehicle. The access device may be attached to the walkway near the entry door to the cabin.
Retractable access systems of different configurations are presently known and have two final positions namely the deployed position and the retracted position. The major types of access devices are the vertical variable height access system and the swing access system.
The vertical variable height access system would generally be used for large excavators and earth moving equipment. In the vertical variable height access system, the ladder or stairs would be operated vertically and would remain vertical both in the deployed position and retracted position. In the swing access system the ladder or stairs when operated will swing up or down to reach either the retracted position or deployed position respectively.
The basic constituents of any access system include a ladder or stairs and a mechanism to actuate the ladder or stairs. The ladder or stairs are generally made of metal such as steel or aluminium. The movement of the ladder or stairs in any access system is controlled by an actuator mechanism. The actuator mechanism moves the ladder or stairs between the deployed and the retracted position. This actuator is usually operated either mechanically or hydraulically. The combination of both means is also in practice.
As mentioned earlier the walkways allow an operator to gain access to the driver cabin and the hatch located behind the cabin. The access device is attached to the walkway; therefore the walkway must carry the weight of the access device. Consequently, the walkway must be built stronger to take the weight of the access device. This results in the requirement for wider walkways which possess the major problem of space management. The wider walkways also mean that the weight of the walkway and access device exert a large lever on the side of the equipment. Most equipment has been designed to reduce weight and increase efficiency and is constructed as light as possible, the addition of a walkway and access ladder can damage the structure of the equipment.
In earth moving equipment, the ladder or stairs possess a problem of access management near the hatch area. The two major members of the ladder (the two lengthy vertical stiles and a number of horizontal rungs) when in a retracted position can block access to the hatch of the earth moving equipment vehicle. If any of the control units in the hatch area break down, trouble shooting is difficult until the access system is in a deployed position.
As mentioned, actuator systems of the access system are generally housed in the hatch of the vehicle and in situations wherein the actuator mechanism of the access systems fails, the operator has restricted or no access to the hatch. Hence the operator has to attend to the problem by removing the ladder mechanically, which adds to the down time of the vehicle.
The access device can be electrically powered or powered by a separate hydraulic system and hence requires an equipment cabinet in close proximity to the access device. The location of the equipment cabinet in close proximity to the access device adds to the space management problem.